Spikes on triangle wave in VCO

[alsetalokin4017]

Having a resistor (e.g. 1 K range) in the gate line of the FET could also help to reduce the spike with relatively slow OPs. It slows down the signal to the FET but keeps the square signal fast. The 7555 as a schmidt trigger is a good idea.

This actually made things a little worse for my test setup using the LM358.

[Lee Leduc]

This is discussed in detail in Walter Jung's book "Op Amp Applications Handbook". This book is available as a free download from Analog Devices.
http://www.analog.com/library/analogdialogue/archives/39-05/op_amp_applications_handbook.html

Attached are the relevant pages (579 through 581).